This invention relates generally to switching devices, and more particularly, to a self arc-extinguishing gas-type switch which utilizes a high pressure fluid pressurized by an arc across contact members to extinguish the arc.
A prior art self arc-extinguishing switch is illustrated in FIG. 1, where an end plate 1 mounted to an insulating cylinder 15, and has one end connected to a line 2, and the other end forming a stationary contact member 3. A member 4 forms an arc-extinguishing fluid containing pressurizing chamber 12, one end thereof being mounted to the end plate 1 and the other end 52 thereof forming a flat plate provided with an opening 5. A heat resisting, insulating member 6 has one end 53 mounted to the end plate 4, and the other end 54 cylindrical and opened. A movable rod 7 has one end forming a movable contact member 55 capable of contacting the stationary contact member 3 and the other end connected to an operating device (not shown). A communicating hole 8 is disposed in the movable rod 7, and a finger contact 9 is mounted to a terminal plate 10. A lead 11 is connected to the terminal plate 10. The terminal plate 10 is mounted to an insulating cylinder 15, and a sliding member 14 is disposed on that portion of the terminal plate 10 into which the movable rod 7 is fitted.
The conventional switching device is constructed as described above and during the closure a current flows from the line 2 through the end plate 1, the stationary contact 3, the movable contact 55, the rod 7, the finger contact 9, and the terminal plate 10 to the lead 11. In the opening operation the movable rod 7 is drawn downwardly by the operating device and an arc 13 is generated between the stationary 3 and movable 7 contacts. This arc generating space blocks off the cylindrical portion 54 at the extremity of the member 6 with a high temperature high pressure fluid while at the same time the energy of the arc itself pressurizes the arc extinguishing fluid 51 in the pressure chamber 12. However, for alternating current, the spontaneous zero point exists. As the zero point is approached, the arc current decreases and the blockage is released to put the arc space under a low pressure. Thus, the arc extinguishing fluid 51, confined in the pressure chamber 12 and put under a high pressure, is conversely blown against the arc 13 to extinguish the arc 13 at the zero point while the cooling action is performed.
Because in the so-called arc-extinguishing type switch the interruption is effected by increasing the pressure of the arc extinguishing fluid with energy possessed by the current which itself is intended to be interrupted, as described above, there has been the disadvantage that, for low interrupting currents, the pressure in the pressure chamber 12 is not sufficiently raised and an effective stream of fresh arc extinguishing fluid, required for the interruption, cannot be blown against the arc. This has resulted in the disadvantage that the interruption of high currents cannot be compatible with that of low currents because the pressure in the chamber 12 is not raised sufficiently with the interruption of low current because the volume of the pressure chamber 12 is sized to ensure sufficiently of the arc extinguishing fluid required for high current arcs to be extinguished.
Futher, there has been the disadvantage that in conventional devices the interrupting capacity is limited. This occurs because, even though the volume of the pressure chamber 12 increases, the communicating hole 8 is disposed only on the movable side, so that the discharge of the high temperature fluid of poor arc-extinguishing property in the arc space and of floating conductive particles vaporized by the arc from metals constituting the contact members is not sufficient.
The present invention aims to provide an arc extinguishing chamber in a switching device which as well as making an improvement of the small current interrupting capability in self arc-extinguishing chambers also makes the interruption of large currents easier.